Generally described, a metal-air cell, such as a zinc-air cell, uses an air permeable cathode separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the cathode to produce hydroxide ions while the metallic zinc is oxidized at the anode to react with the hydroxide ions. Water and electrons are released in this reaction to provide electrical energy.
As compared to conventional types of electrochemical cells, metal-air battery cells provide relatively high power output and lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as a reactant in the electrochemical process rather than a heavier material such as a metal or metallic composition. One drawback, however, with the current design of metal-air cells is that the cells tend to be somewhat larger in size than conventional electrochemical cells. This size constraint is caused by the requirement of having an anode, a cathode, an electrolyte, a cell casing of some sort, and an air passageway to provide reactant air to the cell. For example, a typical metal-air "button"-type cell is found in U.S. Pat. No. 5,451,473, showing an anode can or container, a metal zinc gel or powder within the anode can, a cathode can, an air cathode within the cathode can, an air passageway with an air membrane, and several internal support and sealing structures. Each of these elements is necessary for the cell to operate and requires a certain amount of space.
Although metal-air cells are preferred because of the higher power output, longer life, and lower weight as compared to conventional electrochemical cells, the size of typical metal-air cells has prevented wide spread use of such metal-air cells in many types of applications. There is a need, therefore, for a metal-air cell with a reduced size but with the traditional metal-air advantages and capabilities. In other words, a metal-air cell in the size and shape of a conventional electrochemical cell. Such a cell would have broad availability for many different types of applications. These goals must be accomplished in a cell that remains light-weight and relatively inexpensive for wide spread consumer use.